PDF Encryption failed

I am trying to encrypt PDF file. But after encryption when I open output file it has plain data instead of encryption data. I checked Encrypt call, it returned 1, EncryptStatus also returned 1, which shows encryption was success.

    DebenuPDFLibraryDLL1711 DPL("DebenuPDFLibraryDLL1711.dll");
    DPL.LoadFromFile(L"2020news.pdf", L"");
    int iNumPages = DPL.PageCount();
    int EncPerm = DPL.EncodePermissions(1, 1, 1, 1, 1, 1, 1, 1);    
    //DPL.SetOrigin(1);

    int ret = DPL.Encrypt(L"",L"", 3, EncPerm);
    int st = DPL.EncryptionStatus(); 
    if (ret != 1) {
        int err = DPL.LastErrorCode();
    }

    // Attempt to save the file
     if (DPL.SaveToFile(L"hello-world2.pdf") == 1)  {
          // Display message that the 'Hello Word' file has been written successfully
    }

What am I missing here? Why encryption data was not written to outputfile? I mimicked code from "Foxit Quick PDF Library 17 Developer Guide.pdf"